Methods and compositions for improving stability of biodiesel and blended biodiesel fuel

ABSTRACT

Methods and compositions for improving stability of biodiesel fuel. The methods comprise adding to said biodiesel fuel, an effective amount of a combined treatment that includes a (I) hindered phenol and (II) a Mannich reaction product. The compositions comprise I and II dissolved or dispersed in an organic solvent.

FIELD OF THE INVENTION

The present application is directed to methods and compositions for improving the stability of 100% biodiesel fuels and blended biodiesel fuels during both storage and in engine usage.

BACKGROUND

Biodiesel fuels are becoming increasing popular as an alternative to petroleum based fuel sources. Increasing usage of biodiesel fuel either by itself or in blends with traditional petroleum based (i.e., blended biodiesel fuels) fuel has been seen in diesel engines that are used, for example, in motor vehicles, ships, boats, and power stations. Biodiesel is typically produced from the transesterification of vegetable oils, animal fats, and used cooking oils. One process for producing biodiesel may be seen in U.S. Pat. No. 5,354,878. Raw materials for production of biodiesel fuel include, but are not limited to, soybean oil, corn oil, coconut oil, peanut oil, palm oil, fish oil, lard, mustard seed oil, camelina oil, jojoba oil, hemp oil, poultry fat, safflower oil, jatropha oil, rapeseed oil, tallow, cottonseed oil, frying oil, and others. The transesterification results in the formation of mono-alkyl esters of the corresponding long chain fatty acids and must conform to ATSM D 6751 or EN 14214 specifications. Biodiesel refers to the pure fuel before blending with diesel fuel. Blended biodiesel fuels are denoted as “Bxx” with the “xx” component in the notation representing the percentage of biodiesel in the blend. For example, B40 means 40% biodiesel, 60% petroleum diesel.

Due to the oxidative degradation of the fatty acid esters that may be accelerated by UV light, heat, trace metal presence, and other factors, the fuel often becomes “rancid” or unstable, leading ultimately to sludge and gum formation, thus destroying its intended usage as a fuel source. This degradation results in a marked increase in the amount of filterable solids present in the fuel thereby clogging fuel filters and otherwise leading to pluggage problems in fuel lines and injectors associated with the engine.

SUMMARY OF THE INVENTION

In accordance with the invention, the stability of biodiesel fuels is improved by adding a combined treatment of I and II to the biodiesel fuel or blended biodiesel fuel. I is a hindered phenol, and II is a Mannich reaction product. From about 50-2,500 ppm of hindered phenol (I) is added to the biodiesel fuel or blended biodiesel fuel with about 1-100 ppm of the Mannich reaction product (II) added. Compositions of I or II in an organic solvent such as highly aromatic naptha, kerosene, or a similar hydrocarbon solvent, may be added to the requisite biodiesel fuel or blended biodiesel fuel.

DETAILED DESCRIPTION

The inventive treatment comprises a combination of additives; namely, I. a hindered phenol, and II. a Mannich base. The combined treatment is added to the biodiesel fuel or blended biodiesel. By hindered phenol, we mean a phenolic compound having substituents located at both of the ortho positions relative to the hydroxyl group. A wide variety of such substituents may be present. Additionally, in some cases, a para position substituent may be present as well. For example, the ortho and para position substituents may comprise C₁-C₂₀ alkyl, C₁-C₃₀ alkaryl, substituted C₁-C₃₀ alkaryl, thiophenol, substituted thiophenol, C₁-C₄₀ alkanoic acid ester, C₁-C₆ alkylamino, polynuclear aryl, substituted polynuclear aryl, C₁-C₆ alkoxy, and amine groupings.

The hindered phenols in accordance with the invention may be represented by the formula

wherein R₁ and R₂ may be the same or different, with R₁ and R₂ being independently chosen and selected from the group of C₁-C₂₀ alkyl, C₁-C₃₀ alkaryl, and substituted C₁-C₃₀ alkaryl; n is 0 or 1; R₃, when present, may be selected from C₁-C₂₀ alkyl, thiophenol, substituted thiophenol, C₁-C₄₀ alkanoic acid ester, C₁-C₃₀ alkaryl, substituted C₁-C₃₀ alkaryl, C₁-C₆ alkylamino, C₁-C₆ alkoxy, amine, polynuclear aryl and substituted polynuclear aryl.

At present, preferred hindered phenols include 2,4-di-tertbutyl hydroxytoluene (BHT), and 2,6-di-tertbutylphenol (DTBP).

Other hindered phenols that may be listed as exemplary include 4,4′thiobis-(6-t-butyl-2-methylphenol), octadecyl 3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)-propionate.

-   4,4′-methylenebis(2,6-di-t-butylphenol) -   1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenxyl)benzene -   2,6-di-t-butyl-α-dimethylamino-p-cresol -   2,6-di-t-butyl-4-secbutylphenol -   2,2′-methylenebis(4-ethyl-6-t-butylphenol) -   2,2′methylenebis(4-methyl-6-t-butylphenol) -   2,2′methylenebis(6-(1-methylcyclohexyl)-p-cresol; and -   2,2′-methylenebis(4-methyl-6-cyclohexylphenol)

The Mannich reaction product (II) which is to be conjointly used with the hindered phenol (I) is a condensation product formed via reaction of components II(A), II(B), and II(C), wherein II(A) is an alkyl substituted phenol of the structure

wherein R₄ and R₅ are the same or different and are independently selected from alkyl, aryl, alkaryl, or arylalkyl of from about 1 to 20 carbon atoms, x is 0 or 1.

II(B) is a polyamine of the structure

wherein Z is a positive integer, R₆ and R₇ may be the same or different and are independently selected from H, alkyl, aryl, aralkyl, or alkaryl having from 1 to 20 carbon atoms, y may be 0 or 1.

II(C) is an aldehyde of the structure

wherein R₈ is selected from hydrogen and alkyl having from 1 to 6 carbon atoms.

As to the exemplary compounds falling within the scope of Formula II(A) supra, p-cresol, 4-ethylphenol, 4-t-butylphenol, 4-t-amylphenol, 4-t-octylphenol, 4-dodecylphenol, 2,4-di-t-butylphenol, 2,4-di-t-amylphenol, and 4-nonylphenol may be mentioned. At present, it is preferred to use 4-nonylphenol as the Formula II(A) component.

Exemplary polyamines which can be used in accordance with Formula II(B) include ethylenediamine, propylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine and the like with ethylenediamine being preferred.

The aldehyde component II(C) can comprise, for example, formaldehyde, acetaldehyde, propanaldehyde, butrylaldehyde, hexyldehyde, heptaldehyde, etc. with the most preferred being formaldehyde which may be used in its monomeric form, or more conveniently in its polymeric form (i.e., paraformaldehyde).

As is conventional in the art, the condensation reaction may proceed at temperatures from about 50° to 200°, with a preferred temperature range being about 75′-175° C. As is stated in U.S. Pat. No. 4,166,726, the time required for completion of the reaction usually varies from about 1-8 hours, varying of course with the specific reactants chosen and the reaction temperature. U.S. Pat. No. 4,166,726 is incorporated by reference herein. As to the molar range of components (A):(B):(C) which may be used, this may fall within 0.5-5:1:0.5-5.

The presently preferred Mannich reaction product is prepared by heating p-nonylphenol, ethylendiamine, and paraformaldehyde in a molar ratio of 2:1:2 in xylene until the required amount of water is removed by azeotropic distillation with xylene. The remaining xylene is then removed and an appropriate amount of heavy aromatic naptha is added to make up a 75% active solution.

The combined treatment is added to the requisite biodiesel fuel or blended biodiesel fuel (i.e., B₁-B₉₉) in an amount effective to increase the shelf life or stability of the fuel. More particularly, the components are added to the biodiesel fuel or biodiesel blend in the following amounts:

I. Hindered Phenol

Exemplary addition rate—100-2,500 ppm (I) per one million parts fuel.

Preferred addition rate—250-750 ppm.

II. Mannich Product

Exemplary addition rate—1-100 ppm (II) per one million parts fuel.

Preferred addition rate—5-25 ppm.

The components (I) and (II) may be fed to the requisite biodiesel fuel either separately or in combination. The latter may be accomplished in a one barrel approach wherein I and II are dissolved or dispersed in an organic solvent such as heavy aromatic naptha, toluene, xylene, etc. If a combined approach is desired, I and II may be dissolved or dispersed in the organic solvent in amounts proportioned to correspond to the appropriate ppm feed rate of the components I and II to the biodiesel fuel or blended biodiesel fuel. Presently, a product of about 9.75:1 (I):(II) by weight is preferred, diluted in highly aromatic naptha, kerosene, or similar hydrocarbon solvent. Exemplary compositions comprise from about 5-15:1 I:II by weight dissolved or dispersed in an organic solvent.

EXAMPLES

The invention will now be further described with reference to a number of specific examples which are to be regarded solely as illustrative and not as restricting the scope of the invention. Comparative examples are designated with letters, while examples that exemplify the invention are given numbers.

Example 1

Tests were undertaken in accord with EN 14112, a.k.a. the Rancimat Test. The test is carried out by passing a steady stream of air through the heated (110° C.) sample and measuring the volatile oxidation species produced over a period of time. The point at which the rate of production of these volatile oxidation species reaches a maximum is defined as the induction period or oxidation stability, measured in hours at the given temperature.

Results are shown in Table I. The higher the hours resulting from the test, the longer the biodiesel “lasted” until it became rancid. Therefore, increasing the Rancimat test result number improves the biodiesel.

TABLE 1 Expected Hrs added result if no Resulting Actives Rancimat to stability synergy synergy delivered ppm Result by between AO hrs Number Treatment primaryAO Actives MD (hr) treatment and MD gained C₁ None 0 0 3.03 na na C₂ BHT 500 0 4.17 1.14 na 1 BHT + MD 500 12 4.91 1.88 4.44 0.47 C₃ DTBP 500 0 4.12 1.09 na 2 DTBP + MD 500 12 4.78 1.75 4.39 0.39 C₄ MD 0 12 3.30 0.27 BHT = butylated hydroxy toluene, 2,4-di-tert-butyl-hydroxytoluene DTBP = 2,6 di-tert-butyl phenol MD = Mannich Reaction Product; p nonyl phenol:ethylendiamine:paraformaldehyde 2:1:2 molar ratio

As evidenced in the above table, the inventive combinations delivered more stability time than expected based on individual results of either (AO) (both ˜4.1 hours) and the individual MD (3.3 hours).

Example 2

For these series of tests, the procedures set forth in ASTM D2274 were utilized. This test method measures the insolubles in fuels under specified oxidizing conditions at 95° C. In particular, the method calculates the total insoluble mass (mg/100 mL) as the sum of the filterable insolubles and the adherent insolubles.

As used in the following table, the term “filterable insolubles” is the material produced in the course of stressing the fuel under conditions of this test that is then removable from the fuel by filtering after the test cell has been rinsed with hydrocarbon solvent. The “adherent insolubles” is the material that adheres to the glassware after the fuel has been stressed under the test conditions and flushed from the system with hydrocarbon solvent. “Total insolubles” is the sum of the adherent and filterable solids.

“Iso-octane insolubles” is run only on B100 and is the solids that precipitate from the filtrate plus iso-octane. These are the insolubles that are indicative of the particulates that may form in non-polar solvents, such as petroleum diesel fuel. Accordingly, the iso-octane insoluble test is an indicator of the B100's ability to mix with other normal diesel distillate streams, which are inherently non-polar.

Results are shown in Table 2. Lowering the total filterable insolubles and/or filterable insolubles in biodiesel provides a much more commercially accepted biodiesel. An additive's ability to lower the isooctane insolubles in a B100 biodiesel indicates that a reduction in insolubles will occur upon blending of that B100 biodiesel into other fuels, such as middle distillates, e.g., diesel, to create B₁-B₅₀ and above. The lower the isooctane insolubles, the better the biodiesel.

TABLE 2 Expected filterable Expected Insols if Expected Expected Iso no Adherent Total Octane synergy Insols if Insols if Insoluble Treatment Actives ppm Filterable Adherent Total Iso-Octane between no no if no into B100 primary Actives insol Insoluble Insolubles Insoluble AO and synergy synergy synergy No. SoyBiodiesel AO MD mg/100 ml mg/100 ml mg/100 ml mg/100 ml MD AO-MD AO-MD AO-MD C-5 None 0 0 12 2 14 110 (control) C-6 BHT 500 0 5.1 3.3 8.4 37.5 3 BHT + MD 500 12 0.1 3.0 3.1 9.0 8.65 2.40 11 70 C-7 DTBP 500 0 3.1 0.5 3.6 42.9 4 DTBP + MD 500 12 2.0 0.3 2.3 7.0 7.65 1.0 9 72 C-8 MD 0 12 12.2 1.5 13.7 101.6

Table 2 demonstrates the unexpected properties of the inventive, combined AO/MD treatment in reducing filterable insolubles. Expected filterable insolubles of the BHT/MD combination is more than the filterable insolubles resulting from BHT alone. However, the combination results in only 0.1 filterable solubles being formed, which is a significant reduction (5.1 to 0.1). The B100, as is, with the inventive additives added thereto can be used with more confidence since the total insolubles are decreased significantly (14 vs. ˜2-3 mg/ml).

The isooctane insolubles reduction from the tested inventive AO/MD combinations further demonstrate the unexpected nature of the invention. This reduction will allow B100 to be blended with significant confidence into normal distillate hydrocarbon fuels, with low insoluble levels being formed during prolonged storage or during normal heat cycling in an operating engine. The B100 fuel, without addition of the inventive AO/MD treatment, would be expected to have total insolubles in the 70 mg/ml range. In sharp contrast, as shown in the above Table 2, total insolubles were below 10 mg/ml.

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention. 

1. Method for improving the stability of biodiesel fuel comprising adding to said biodiesel fuel an amount effective for the purpose of (I) a hindered phenol and (II) a Mannich reaction product.
 2. Method as recited in claim 1 wherein (I) is added in an amount of about 50-2,500 ppm based upon one million parts of said biodiesel fuel and wherein (II) is added in an amount of about 1-100 ppm based upon one million parts of said biodiesel fuel.
 3. Method as recited in claim 2 wherein said biodiesel fuel is blended with petroleum diesel fuel.
 4. Method as recited in claim 2 wherein said hindered phenol (I) has the formula

wherein R₁ and R₂ may be the same or different and each is independently chosen from C₁-C₂₀ alkyl, C₁-C₃₀ alkaryl and substituted alkaryl; n is 0 or 1; R₃, when present is selected from C₁-C₂₀ alkyl, thiophenol, substituted thiophenol, C₁-C₄₀ alkaneoic acid ester, C₁-C₃₀ alkaryl, substituted C₁-C₃₀ alkaryl, C₁-C₆ alkylamino, C₁-C₆ alkoxy, amine, polynuclear aryl and substituted polynuclear aryl.
 5. Method as recited in claim 4 wherein said Mannich reaction product II is formed via reaction of components II(A), II(B), and II(C) wherein component IIA has the formula

wherein R₄ and R₅ are the same or different and are independently selected from alkyl, aryl, alkaryl or arylalkyl of from about 1 to about 20 carbon atoms and x is 0 or 1; wherein component II(B) has the formula

wherein Z is a positive integer, R₆ and R₇ may be the same or different and are independently selected from H, alkyl, aryl, araalkyl or alkaryl having from 1 to 20 carbon atoms, y may be 0 or 1; and wherein component II(C) is an aldehyde having the structure

wherein R₈ is selected from H and alkyl having from 1 to 6 carbon atoms.
 6. Method as recited in claim 5 wherein in said Mannich reaction product II, said components are present in a molar ratio II(A):II(B):II(C) of 0.5-5:1:0.5-5.
 7. Method as recited in claim 6 wherein said hindered phenol (I) is a member selected from the group consisting of BHT and DTBP and mixtures thereof.
 8. Method as recited in claim 6 wherein said component II(A) of said Mannich reaction product (II) is a member or members selected from the group consisting of p-cresol, 4-ethylphenol, 4-t-butylphenol, 4-t-amylphenol, 4-t-octylphenol, 4-dodecylphenol, 2,4-di-t-butylphenol, 2,4-di-t-amylphenol, and 4-nonyl-phenol.
 9. Method as recited in claim 6 wherein said component II(B) of said Mannich reaction product is selected from the group consisting of ethylenediamine and triethylenetetraamine.
 10. Method as recited in claim 6 wherein said component II(C) of said Mannich reaction product is selected from the group consisting of formaldehyde and paraformaldehyde.
 11. Method as recited in claim 6 wherein said component II(A) of said Mannich reaction product is 4-nonylphenol, said component II(B) of said Mannich reaction product is ethylenediamine and said component II(C) of said Mannich reaction product is formaldehyde or paraformaldehyde, said II(A):II(B):II(C) being present in a molar ratio II(A):II(B):II(C) of 2:1:2.
 12. Composition for stabilizing a biodiesel fuel, said composition comprising (I) and (II) dispersed or dissolved in an organic solvent, (I) being a hindered phenol and (II) being a Mannich reaction product.
 13. Composition as recited in claim 12 wherein said components (I) and (II) are present in said composition in a weight ratio of about 5-15:1 (I):(II).
 14. Composition as recited in claim 13 wherein said hindered phenol (I) has the formula

wherein R₁ and R₂ may be the same or different and each is independently chosen from C₁-C₂₀ alkyl, C₁-C₃₀ alkaryl and substituted alkaryl; n is 0 or 1; R₃, when present is selected from C₁-C₂₀ alkyl, thiophenol, substituted thiophenol, C₁-C₄₀ alkaneoic acid ester, C₁-C₃₀ alkaryl, substituted C₁-C₃₀ alkaryl, C₁-C₆ alkylamino, C₁-C₆ alkoxy, amine, polynuclear aryl and substituted polynuclear aryl.
 15. Composition as recited in claim 14 wherein said Mannich reaction product (II) is formed via reaction of components II(A), II(B), and II(C) wherein component II(A) has the formula

wherein R₄ and R₅ are the same or different and are independently selected from alkyl, aryl, alkaryl or arylalkyl of from about 1 to about 20 carbon atoms and x is 0 or 1; wherein component II(B) has the formula

wherein Z is a positive integer, R₆ and R₇ may be the same or different and are independently selected from H, alkyl, aryl, araalkyl or alkaryl having from 1 to 20 carbon atoms, y may be 0 or 1; and wherein component II(C) is an aldehyde having the structure

wherein R₈ is selected from H and alkyl having from 1 to 6 carbon atoms.
 16. Composition as recited in claim 15 wherein in said Mannich reaction product (II), said components are present in a molar ratio II(A):II(B):II(C) of 0.5-5:1:0.5-5.
 17. Composition as recited in claim 16 wherein said hindered phenol (I) is a member selected from the group consisting of BHT and DTBP and mixtures thereof.
 18. Composition as recited in claim 17 wherein said component II(A) of said Mannich reaction product (II) is a member or members selected by the group consisting of p-cresol, 4-ethylphenol, 4-t-butylphenol, 4-t-amylphenol, 4-t-octylphenol, 4-dodecylphenol, 2,4-di-t-butylphenol, 2,4-di-t-amylphenol, and 4-nonyl-phenol; said component II(B) of said Mannich reaction product is selected from the group consisting of ethylenediamine and triethylenetetraamine; and wherein said component II(C) of said Mannich reaction product is selected from the group consisting of formaldehyde and paraformaldehyde.
 19. Composition as recited in claim 18 wherein said component II(A) of said Mannich reaction product is 4-nonylphenol, said component II(B) of said Mannich reaction product is ethylenediamine and said component II(C) of said Mannich reaction product is formaldehyde or paraformaldehyde, said II(A):II(B):II(C) being present in a molar ratio II(A):II(B):II(C) of 2:1:2.
 20. Composition as recited in claim 19 wherein said organic solvent is heavy aromatic naptha. 